The present Application claims priority of Japanese Patent Application Ser. No. 11-50930 filed on Feb. 26, 1999.
1. Field of the Invention
The present invention relates to an oxide superconductive wire and a superconductive device using an oxide superconductor.
2. Discussion of the Background
Oxide superconductors based on systems such as Yxe2x80x94Baxe2x80x94Cuxe2x80x94O, Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O, or Tlxe2x80x94Baxe2x80x94Caxe2x80x94Cuxe2x80x94O yield high critical temperatures not lower than the boiling point of liquid nitrogen, and are hence of high industrial value because they allow the use of an inexpensive liquid nitrogen as the cooling medium instead of the expensive liquid helium or can be easily cooled to the superconductive state by using a compact freezer.
Such oxide superconductors should be first processed into wires to ease their use in the practical application field of energy. As the effective means for processing them into wire materials, there are known methods of fabricating tape-like superconductive wires by forming superconductive films on a metallic tape by, for instance, a coating method, a vapor phase growth method, or a liquid phase growth method.
For example, there is known a wire material using Hastelloy alloy having excellent heat resistance or silver, which undergoes little reaction with an oxide superconductive wire as a metallic tape. In case of using the materials above, a variety of attempts have been made to obtain oxide superconductors with highly oriented crystals because this is essential to realize high critical current density.
In the case of using Hastelloy, a method comprising fabricating a buffer layer using yttrium-stabilized zirconia (YSZ), MgO, etc., by a particular method has been studied in order to grow a superconductive film having a high crystallographic orientation and yet free from-reaction with the oxide superconductor during the formation of the film. This method realizes a critical current at a practically sufficient high density. However, this is not always the most suitable method for fabricating long wire materials because it requires a complicated production process.
The method using silver as the metallic tape, on the other hand, is expected to be promising for obtaining long wire materials by a simple process because silver is less reactive with an oxide superconductor and because a film of the oxide superconductor can be directly deposited thereon. Recently, as disclosed in, for example, Japanese Patent No. 2813287, critical current is available at a practically high density level by using a tape comprising a collective texture of superconductors formed on the (100) and (110) planes of thermally treated silver. According to the disclosure, there is also described a metallic tape using a complex alloy of the elements which hardly forms a solid solution with silver; i.e., iron, nickel, or chromium, as the core material, and silver is formed thereon. By using the metallic tape having the constitution above, a tensile strength higher than that comprising silver alone can be obtained. Such a metallic tape can be handled more easily, and, moreover, it may provide a critical current at a higher effective density because the thickness thereof can be reduced.
In case of using the complex alloys above as the metallic tapes for forming thereon thin films of oxide superconductors, the present inventors recently found that the adhesion strength between the silver layer and the core material is not always sufficiently high in case the tape is processed into a thinner tape and subjected to the film deposition process, and problems of peeling off are found to occur on the silver layer.
In the light of the aforementioned circumstances, a first aspect of present invention provides an oxide superconductive wire comprising a first metallic layer, a second metallic layer, and an oxide superconductor layer. The first metallic layer is made of silver based alloy consisting essentially of silver and a metal selected from the group consisting of copper, antimony, tin, germanium, gallium, indium, zinc, platinum and palladium. The second metallic layer is fixed on the first metallic layer and has a tensile strength higher than that of silver. The oxide superconductor layer is formed on said first metallic layer.
In the first aspect of the present invention, the second metallic layer may consist essentially of nickel, iron, or chromium.
In the first aspect of the present invention, the second metallic layer may be made of nickel based alloy, and the nickel based alloy may consist essentially of nickel and an element selected from the group consisting of aluminum, copper, chromium, manganese, silicon, antimony, and zinc.
In the first aspect of the present invention, the second metallic layer may be made of silver based alloy.
In the first aspect of the present invention, the first metallic layer may cover the second metallic layer.
In the first aspect of the present invention, the first metallic layer may be oriented along the crystallographic (110), (100), or (210) plane.
In the light of the aforementioned circumstances, a second aspect of the present invention provides an oxide superconductive wire comprising a first metallic layer, a second metallic layer, and an oxide superconductor layer. The first metallic layer is made of silver based alloy consisting essentially of silver and a metal selected from the group consisting of copper, antimony, tin, germanium, gallium, indium, zinc, platinum and palladium. The second metallic layer is made of sintered alloy consisting essentially of silver powder and powder of nickel, iron, chromium, or nickel based alloy. The nickel-based alloy consists essentially of nickel and an element selected from the group consisting of aluminum, copper, chromium, manganese, silicon, antimony, and zinc. The second metallic layer has a tensile strength higher than that of silver, and is fixed on the first metallic layer. The oxide superconductor layer is formed on the first metallic layer.
In the second aspect of the present invention, the first metallic layer may be oriented along the crystallographic (110), (100), or (210) plane.
In the second aspect of the present invention, the first metallic layer may cover the second metallic layer.
In the light of the aforementioned circumstances, a third aspect of the present invention provides an oxide superconductive wire comprising a first metallic layer, a second metallic layer, and an oxide superconductor layer. The first metallic layer consists essentially of silver and oriented along crystallographic (210) plane. The second metallic layer has a tensile strength higher than that of silver and is fixed to the first metallic layer. The oxide superconductor layer formed on the first metallic layer.
In the third aspect of the present invention, the first metallic layer may cover the second metallic layer.
In the third aspect of the present invention, the second metallic layer may be made of silver based alloy.
Each of oxide superconductive wires of the first, second, and third aspects of the present invention might be provided in a superconductive device. In the superconductive device, the oxide superconductive wire may be coiled so that the oxide superconductor layer is disposed on the inner side of the coiled wire and the oxide superconductive wire may be covered with an insulator layer.
The tensile strength of the second metallic layer of each of the aspects may be found about by measuring the tensile strength of replica of the material of the second metallic layer. Well-known analysis apparatus may measure the material of the second metallic layer from information of the cross sectional surface of the second metallic layer.
The silver based alloy of each of the first and the second aspects of the present invention contains silver of more than 50 atomic % of its whole body.
Above mentioned crystallographic plane orientation of the first metallic layer of the each aspect of the present invention, the (110), (100), or (210) plane is oriented such that each plane may be parallel to the first metallic layer.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in accompanying drawings.